We propose to induce chemically, and to isolate, mutants of somatic mammalian cells (human and rodent) with defects or alterations in RNA polymerase activity. The mutants will be selected primarily on the basis of drug-resistance (e.g., alpha-amanitin, toyocamycin and rifamycin). A series of independently arising mutants will be isolated by a variety of mutagenic and selective procedures; each mutant will be purified by re-cloning, and its phenotype (e.g. drug-resistance) verified. The mutants will then be subjected to extensive biochemical and genetic characterization. The genetic analyses will be facilitated by isolating the mutants in cell lines that are readily hybridized. Hybrids between pairs of similar mutants, and between each mutant and its wild-type counterpart, will be used for the analysis of complementation relationships, dominance and recessiveness, and chromosomal gene location. The mapping procedures will be so designed as to give the location of the mutant genes in the human rather than rodent karyotype. The complementation analyses will permit the determination of the minimum number of genes involved in each function; the dominance and mapping analyses will permit some inferences to be drawn concerning gene actions -- for example, dominant drug-resistnace suggests an altered affinity for the drug of the target molecule. The mutants resistant to inhibitors of RNA polymerases (alpha- amanitin, toyocamycin, rifamycin will be characterized in terms of sensitivities of the isolated RNA polymerases, and the pattern of RNA species synthesized in the presence and absence of the drugs. Altered enzymes will be isolated and purified, and their sub-unit structures compared with that of the wild-type enzymes.